The present invention relates to power converter apparatus and methods, and more particularly, to apparatus and methods for power transfer between AC and DC busses.
AC/DC power converters are used in a variety of applications, including in DC power supplies and uninterruptible power supplies (UPSs). For example, a UPS may include an input rectifier that is used to convert AC voltage from an AC source, such as a utility source, to a DC voltage on a DC bus, which can also be powered from an auxiliary source, such as a battery. The DC voltage may be provided directly to loads, as is common in telecommunications applications, and/or may be converted back to an AC output voltage by an inverter and used to power AC loads, as is common in data processing and industrial applications.
Such input rectifiers may take a variety of different forms. For example, some power converters may include a passive input rectifier, such as a diode bridge, that produces a DC output that generally varies with the AC input voltage. Other power converters use active rectifiers, e.g., transistor bridge circuits that can be controlled to provide regulation of the DC output voltage. A variety of different control techniques may be used in such active rectifier circuits. One conventional technique, described in U.S. Pat. No. 4,366,390 to Rathmann, involves use of a bidirectional converter unit that stabilizes a DC bus voltage by shifting the phase of the AC voltage on the AC bus relative to an AC source coupled to the AC bus.